Ok...did you finish Skull Castle and then go to Brimloch Roon and save, then crash, or was your last save before you even started Skull Castle?
All games are prone to crashing, especially on the Windows platforms, so save, save, save! Repeatedly and often.
One last question: did you, perchance, equip the Vampire Ring? If you're playing an unpatched game, that will crash you every time.
-Sazerac